The present invention concerns the field of digital communication and pertains particularly to efficient generation within a remote base station of a synchronization signal for a cordless communication system.
A cordless telephone system generally includes a fixed part, which connects a telephone network to one or more base stations. Base stations are generally connected to a fixed part by wires, or may be integrated directly with the fixed part. For example, a system may include a master base station and several remote base stations connected by a wire highway to the master base station. Each base station communicates with one or more portable parts, typically a handset, via a radio frequency (RF) signal link. For example, the cordless system may be included in a private branch exchange (PBX) and utilize a cordless telephone system in accordance with the Digital European Cordless Telecommunications (DECT) Common Interface.
For example, the base stations may be connected together using a data highway operating in accordance with a voice coding algorithm such as an Adaptive Pulse Code Modulation (ADPCM) highway. An ADPCM highway utilizes four wires to connect the base stations. For each base station, one wire carries a synchronization signal (ADPCM.FS), one wire carries a clock signal (ADPCM.CLK), one wire carries data in to the base station (ADPCM.DIP) and one wire carries data out from the base station (ADPCM.DOP).
When a system includes more than one base station which utilize the DECT common interface, each base station must transmit messages in synchronization with a system wide DECT frame synchronization signal. In order to assure proper synchronization, the DECT frame synchronization signal is forwarded by a master source to each remote base station over a dedicated wire.
In accordance with the preferred embodiment of the present invention, a first synchronization signal is used by a master base station and a remote base station in a digital cordless communication system. The master base station generates a second synchronization signal. The second synchronization signal is used to transfer information over a transmission medium between the master base station and the remote base station. The master base station generates the first synchronization signal from the second synchronization signal. Information is transferred over the transmission medium between the master base station and the remote base station using the second synchronization signal. The remote base station generates the first synchronization signal from the second synchronization signal. The first synchronization signal is utilized by the master base station and the remote base station for digital cordless communication.
For example, in the preferred embodiment the first synchronization signal is a DECT frame synchronization signal and the second synchronization signal is an ADPCM synchronization signal. Also in the preferred embodiment, the first synchronization signal within the remote base station and the master base station is synchronized using the synchronization information sent from the master base station to the remote base station. For example, this synchronization information includes a current count from a counter used by the master base station to generate the first synchronization signal from the second synchronization signal.
In the preferred embodiment, the remote base station uses a lock window signal to filter out parasitic pulses within the second synchronization signal. When a pulse from the second synchronization signal is absent from a lock window, the absent pulse is reconstructed by the remote base station when the remote base station generates a reconstructed second synchronization signal.
The present invention allows for the generation of a DECT frame synchronization signal from an ADPCM frame synchronization signal. This eliminates the need for a master base station to transfer to remote base stations the DECT frame synchronization signal over a dedicated wire.